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Scientists search for faults in Queensland

ELEANOR HALL: Large earthquakes on the Australian mainland are rare but seismologists are monitoring the development of what could be minor fault lines in north Queensland.

Since the beginning of the year a number of quakes have rattled the region from Innisfail to Mackay and Geoscience Australia says it's been watching every movement in the last month to see if it points to a significant shift in the plates beneath Australia.

Josh Bavas has more.

JOSH BAVAS: It was a Saturday afternoon and Ted Sievers was in his beach house at Cape Upstart when he heard the earthquake rumbling through the mountains.

TED SIEVERS: It's like a shudder closing in around ya. That's what it felt like inside the building, like a great noise sort of closing in on you, you know.

JOSH BAVAS: This particular epicentre was to the west of Bowen with a magnitude similar to a quake which damaged a city in southern Spain earlier this month.

Ted Sievers says he was on edge after the recent disasters around the world.

TED SIEVERS: So I thought during the night if we got a tsunami warning or whatever, the best thing to do was go up the hill. And um I just got a little bit of gear ready in a bag, like a set of shoes, long trousers, bottle of water and a life jacket.

JOSH BAVAS: Emma Mathews is part of a team from Geoscience Australia who's installed specialised equipment around Bowen to record every single aftershock since April's quake.

EMMA MATHEWS: We've currently got some temporary aftershock recorders at four sites south-west of Bowen and the aftershocks that we've recorded on the permanent stations, there's approximately seven.

JOSH BAVAS: She says a one-off quake on the Australian plate is usually followed up by many more smaller shakes.

EMMA MATHEWS: Generally earthquakes tend to occur in clusters around Australia. You get sort of phases of activity depending on the stresses that build up and the release of those stresses and this seems to be one of those examples.

JOSH BAVAS: Ted Sievers says he didn't miss a single aftershock.

(To Ted Sievers) Explain the noise. Where did it start coming from and what happened?

TED SIEVERS: Well I woke up during the night. I think I woke up a couple of minutes before each one of them, probably because I was a bit tensed up from the first, you know. And eight o'clock I think that night was the first one and it was not as bad of course as the first.

JOSH BAVAS: But it's the number and magnitude of these tremors which suggest new minor fault lines are forming near Bowen.

EMMA MATHEWS: They don't occur on subduction zones or plate boundaries like in New Zealand or Japan. We have them on the inside of the plate and this is related to stresses that build up in the tectonic plate.

We'll have to wait and see what the data says before we can declare that there's a new fault line up there.

JOSH BAVAS: It's still worrying news for locals who aren't used to such seismic activity.

TED SIEVERS: But this one, well, you remember it because it shakes you up a bit and probably as you get a bit older it shakes you up a bit more.